In semiconductor manufacture, everyday engineers want to identify trace features or sets of trace features, such as certain pressures, temperatures, gas flows, etc. Those trace features or sets of trace features cause the output of processes in semiconductor manufacture to be out-of-specification or deviated from the targets. For example, a high pressure may cause deposition of a film lower than specification. It is not uncommon to find 5 million potential trace features that need to be distinguished or ranked in a particular run by engineers.
There are many secondary factors or consumables, such as temporal drifts, age of equipment, wearing of polishing pads, environmental factors, and other secondary factors. Frequently, the secondary factors or consumables cause changes of both the trace features and the targets. For example, an old tool in rapid thermal processing (RTP) may have a dirty glass film or it may be fogged up requiring the lamps to consume more power and run hotter.